1. Field of the Invention
This invention relates to a communication node, a communication method, and a computer program. More particularly, even when an inaccessible node occurs in a ring network using a distributed hash table, the invention allows the network to recover automatically by eliminating the inaccessible node.
2. Description of Related Art
In recent years, a P2P (Peer-to-Peer) network, which can ensure scalability by distributing the server function, has become valued increasingly. The P2P network is an overlay network, which is a computer network built over a computer network. It is configured to enable communication without being aware of the IP network topology. When configuring the overlay network, distributed hash technology is used to search a partner (node) to communicate with.
As a representative protocol using the distributed hash technology, Chord is disclosed in “Chord: A Scalable Peer-to-peer Lookup Protocol for Internet Applications” Ion Stoica, Robert Morris, David Liben-Nowell, David R. Karger, M. Frans Kaashoek, Frank Dabek, Hari Balakrishnan, IEEE Transactions on Networking, Vol. 11, February 2003. The Chord is a protocol in which a ring overlay network (hereinafter referred to as a “Chord ring”) is constructed by nodes each having a hash value derived from an IP address as a node ID. All the nodes on the Chord ring have routing information for correctly securing communication paths to the nodes on Chord ring. Here, the next clockwise node is called a successor, and the next anticlockwise node is called a predecessor. The information indicating the successor or the predecessor is used as routing information. When the successor and the predecessor indicate correct nodes in each of the nodes, all the nodes are connected correctly, which means that correctness of the Chord ring is ensured.
In addition, JP-A-2006-195694 discloses distribution of content data using a ring overlay network.